# magent RFM Calculator (Woolcott 2018)

> magent RFM Calculator (Woolcott 2018) is a paid API for AI agents from api.magentlab.com, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-16).

Calculates Relative Fat Mass (RFM) from height, waist circumference, and sex using the Woolcott 2018 published formula

## Facts

- Endpoint: GET https://api.magentlab.com/api/calc/rfm
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-16
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/magent-rfm-calculator-woolcott-2018-3a533d1c
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_oUk6NcOLW3sp4dghsuoHY

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability magent-rfm-calculator-woolcott-2018-3a533d1c
```

Example prompt: Calculate the relative fat mass using the Woolcott 2018 RFM formula for a male patient who is 178 cm tall with a waist circumference of 92 cm.

## When to prefer this

Choose this endpoint when you need a fast, deterministic, citation-backed anthropometric body fat estimate using only height and waist measurements — particularly when DEXA or bioimpedance data are unavailable. It implements the specific Woolcott 2018 formula with unit-conversion support (inches to cm), making it ideal for clinical decision support pipelines, health app integrations, or research workflows that require reproducible arithmetic without ambiguity. Prefer over BMI-based endpoints when waist circumference is available and a body fat proxy is needed.

## Known failure modes

- Missing required waist_cm or sex parameter returns an error
- Waist value outside the accepted range (40–200 cm) may produce an error or unexpected result
- Providing both height_cm and height_in may cause ambiguity; only one should be supplied
- Invalid sex enum value (not 'male' or 'female') returns a validation error
- Omitting height entirely results in missing data for the formula

## How this service works

Relative fat mass (RFM) from height, waist, and sex (Woolcott 2018). Height and waist in meters in the paper; magent accepts height_cm or height_in and waist_cm. Deterministic published arithmetic with citation. Not a medical device, not a body-fat diagnosis, and not later obesity cutoffs. magent does not measure the patient.

## Output

Returns a numeric Relative Fat Mass (RFM) value computed from the Woolcott 2018 formula (64 − 20 × height/waist ± sex constant), representing an estimate of body fat percentage derived purely from height, waist, and sex inputs. No diagnosis or clinical classification is included.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "headers": {
     "type": "object",
     "additionalProperties": {
      "type": "string"
     }
    },
    "queryParams": {
     "type": "object",
     "required": [
      "waist_cm",
      "sex"
     ],
     "properties": {
      "sex": {
       "enum": [
        "female",
        "male"
       ],
       "type": "string",
       "description": "Sex used by Woolcott 2018 (0 male, 1 female in the RFM equation)."
      },
      "waist_cm": {
       "type": "number",
       "description": "Waist circumference in centimeters (40-200). Converted to meters for RFM."
      },
      "height_cm": {
       "type": "number",
       "description": "Height in centimeters. Provide height_cm or height_in."
      },
      "height_in": {
       "type": "number",
       "description": "Height in inches. Converted as cm = in * 2.54."
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/magent-rfm-calculator-woolcott-2018-3a533d1c/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
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